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Near plugs of VGA or DVI cables is often a "plastic" cylinder containing ferrite to protect the signal from interferences. These are called "ferrite cores", "ferrite beads" or "ferrite chokes". It seems a component that low cost cables often do not have.

Looking for a mini DP to VGA / DVI / HDMI adapter, I observed that most models don't have a ferrite core on the mini DisplayPort cable, but that more expensive models from a reputable brand all do have such protection.

I also read that ferrite beads were intended to protect analog signal.

So, I'm wondering in which context are ferrite cores be recommended in general, and on the adapter mini DP cable especially.

  • Are ferrite beads recommended on the mini DP adapter if the VGA or DVI cables connected to the adapter already have ones at both ends?

  • Are ferrite cores only useful for VGA and DVI signals, or also for DP and HDMI?

  • Which are the typical sources of possible interferences with the display signal?

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on the adapter itself, which is less than the length of 5 inches typically, no I don't see the point much less how you could fit it. That is too short a length to worry about getting noise on.

on video cables...

on digital cables such as DP, hdmi, DVI-D I don't see the point.

on vga cables or DVI-I that is operating analog, the ferrite choke's purpose is to dissipate high frequency noise that would corrupt the analog signal along the cable and then reach into the device connected at either end and cause problems. That generally does not happen with digital signals given the nature of how digital signals are processed. If you overloaded a digital signal with noise to where it was a problem I don't see the likelihood of a choke being cable of dealing with it to save the signal.

For a shorter analog cable, the likelihood of noise that happening is much reduced, like the 6' or less from tower to monitor on your desk. If you are running a 15' or longer VGA cable, with the cable in a noisy environment, then the ferrite choke would have some merit. A noisy environment would be the long cable running over or very near a magnetic ballast fluorescent light (not common these days) or near equipment running AC induction motors and the 120-240vAC power cables that connect to them.

If you had a long vga or DP cable, and then had a mini-DP to full-DP adapter for example, given it's all digital I would not fret about finding one to purchase that had a molded in choke on the long cable. And buying an added on choke, very cheap, that you could snap on to the cable at each end (not on the adapter) wouldn't hurt but it's also difficult to say if it's doing anything useful.

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